The present invention relates to a data transfer control system, an electronic instrument, a program, and a data transfer control method.
In recent years, an interface standard called IEEE1394 has attracted attention. A protocol called Serial Bus Protocol-2 (SBP-2) has been proposed as a higher level protocol including a part of the function of the transaction layer of IEEE1394. SBP-2 (SBP in a broad sense) has been proposed to enable a command set of SCSI (SPC-2) to be utilized on the protocol of IEEE1394. The command set which has been used in an electronic instrument conforming to the SCSI standard can be used in an electronic instrument conforming to the IEEE1394 standard by using SBP-2 by merely adding minimum changes to the command set. Therefore, the design and development of an electronic instrument can be facilitated.
In SBP-2, peer-to-peer data transfer is performed between an electronic instrument as an initiator (personal computer, for example) and an electronic instrument as a target (storage device, for example). Therefore, after the initiator logs in to the target and acquires an access right, the initiator exclusively possesses the access right (SBP-2 access right) to the target. Therefore, another electronic instrument cannot access the target.
There may be a case where an expansion device (an expansion electronic instrument) is provided for a notebook type personal computer (hereinafter may be called “PC”) as an option for expanding the function of the notebook type personal computer. A storage device such as a hard disk drive (HDD) and a CD drive and various interfaces such as IEEE1394 and USB are provided to the expansion device. The user can utilize various functions (storage device and port) of the expansion device by connecting the notebook type PC with the expansion device. This eliminates the need to provide the expansion functions of the expansion device to the main body of the notebook type PC, whereby reduction of the weight and size of the notebook type PC can be achieved.
However, in the case of connecting the notebook type PC with the expansion device, if another PC acquires the access right to the expansion device (right to use the bus), the user cannot utilize the expansion functions of the expansion device.